The present invention relates generally to control systems for controlling an implement carried by a machine, and more particularly, to a method and apparatus for controlling a digging implement of a trenching machine while trenching a subsurface of earth.
Trenching machines for trenching the subsurface of earth at a construction site typically include a drive unit mounting some form of a trenching or digging implement, such as a digging chain or rock wheel. When preparing the subsurface of earth for, for example, a drain, a sewer, utility pipes, a cableway and the like, it is typically desirable for the contour or grade of the subsurface shaped by the digging implement to approximate a desired finished surface as closely as possible. How accurately the subsurface of earth is shaped depends upon both how accurately the position of a cutting edge of the digging implement can be determined and maintained, and how accurately the direction of travel of the digging implement can be determined.
A number of prior art systems control the positioning of a tool carried by a machine, including the digging implement of a trencher. For example, conventional control systems use a laser as a reference for positioning the digging implement in a trench. In order to position accurately the digging implement, a laser receiver needs to be mounted directly over the cutting edge of the digging implement. However, the location of the cutting edge of the digging implement is changing constantly during trenching operations. As the pitch of the digging implement changes with digging depth, the mast angle of the laser receiver mounted above the cutting edge is changing similarly, thereby causing inaccurate measurements of the position of the cutting edge of the digging implement. A prior art solution to this problem has been to readjust manually the mast mounting the laser receiver to a vertical position as the pitch of the digging implement changes in order to maintain accuracy during operation. It is to be appreciated that the above mentioned prior art solution is labor intensive, and causes delays in trenching operations as the digging implement must be stop in order for a technician to readjust the mast each time the pitch of the digging implement changes.